The number of n electrons present in 2.6 g of ethyne are:

Ethyne is C2H2There are two π-bonds in ethyne. One bond contains 2 electrons. So, there are 2 x 2 i.e., 4π electrons is one molecule of ethyne.Mol. wt. of CH≡CH=12+1+12+1=26=1 mol  of CH≡CH∴ 26g⋅CH≡CH contain π electrons =4×NA2.6g⋅CH≡CH contain π electrons =4NA×2.626=0.4NA